Reversal of Coherently Controlled Ultrafast Photocurrents by Band Mixing in Undoped GaAs Quantum Wells

Abstract

It is demonstrated that valence-band mixing in GaAs quantum wells tremendously modifies electronic transport. A coherent control scheme in which ultrafast currents are optically injected into undoped GaAs quantum wells upon excitation with femtosecond laser pulses is employed. An oscillatory dependence of the injection current amplitude and direction on the excitation photon energy is observed. A microscopic theoretical analysis shows that this current reversal is caused by the coupling of the light- and heavy-hole bands and that the hole currents dominate the overall current response. These surprising consequences of band mixing illuminate fundamental physics as they are unique for experiments which are able to monitor electronic transport resulting from carriers with relatively large momenta.

Ultrafast shift and rectification photocurrents in GaAs quantum wells: Excitation intensity dependence and the importance of band mixing

“…Without any additional electric or magnetic fields, injection currents do not exist in bulk GaAs, they are, however, present in GaAs quantum wells (QW) with lower symmetry. 10,19,20 Under the action of an optical field that induces interband transitions the electronic charge density in the noncentrosymmetric GaAs crystal is shifted in real space from the As atoms towards the neighboring Ga atoms and this process leads to the so-called shift current.…”

Polarization-induced phase shift of ultrafast photocurrents

“…Microscopically, shift currents and injection currents result from a polar distribution of carriers in real and momentum space, respectively. They are also known as linear and circular photogalvanic currents, since they occur for optical excitation with linearly and circularly polarized light, respectively [1][2][3].Here, we show that the frequency dynamics of the coherent polarization resulting from excitation of discrete transitions is capable of significantly altering this phase rule such that shift and injection currents occur for both, linear and circular polarizations. The measurements are performed on exciton transitions in a (110)-oriented, 5-nm wide GaAs quantum well (QW) sample, with the x, y, and z directions being parallel to the …”

“…Microscopically, shift currents and injection currents result from a polar distribution of carriers in real and momentum space, respectively. They are also known as linear and circular photogalvanic currents, since they occur for optical excitation with linearly and circularly polarized light, respectively [1][2][3].…”

Oscillatory excitation energy dependence of injection currents in GaAs/AlGaAs quantum wells

“…This does not hold for very small photon energies where excitonic effects change the behavior. These experimental findings provide evidence for a reversal of the direction of the injection current at different photon energies [5,6]. For the theoretical description we use a microscopic approach, which is based on a 14x14 k.p band structure theory [7] in combination with multi-subband semiconductor Bloch equations [8].…”